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The NEC seems clear about adding at least 1 ground rod (possibly 2?). However, I was told by local electrical inspector that I don't need a ground rod if I run a full sized ground to my detached garage for a 50 amp sub panel.

I think for protection from lighting strikes, which are common up here in the Adirondacks, I want those ground rods.

Also, can I install #6 bare copper to rebar when foundation is poured? What method of connection to rebar is acceptable if so?

FreeMan
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Brian Kearney
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    The concrete-encased electrode (Ufer ground) all by itself should be better, and more than sufficient, for your additional electrode at the garage, especially if you do a good job tying the steel together and don't concentrate on only meeting the minimum required for that.I believe it's moderately common to bring up a rebar for the connection, but will leave the answering of that to someone else who'll be more certain. Pretty sure that if copper goes into the slab, it has to be insulated copper, and the connection to the rebar has to be listed for concrete encasement. – Ecnerwal May 21 '22 at 00:21
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    @Ecnerwal Great comment, you should make that an answer even if it doesn't directly address the OP's question. And according to NoSparksPlease, jurisdictions are requiring Ufer grounds in new construction, which I concur with. BTW, the ground wire connected to the re-bar needs to be permanently accessible. – George Anderson May 21 '22 at 01:09
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    NEC 250.68(A) Requires connections to electrodes to be accessible, but Ex No.1 excludes concrete encased and direct buried connections. It is not uncommon for AHJ's to make specific modifications to this section, particularly where George lives. – NoSparksPlease May 21 '22 at 01:53
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    A ufer ground requires a 4 awg grounding electrode conductor. 6 awg is allowed for rod pipe and plate electrodes. In reality anyone that has measured a 2nd location can say the overall ground plane has increased and code doesn't state witch direction to measure so when measured it is less than 25 ohms. so a single rod is all that is needed in reality. I have heard those that think the 2nd location can cause additional hazards . – Ed Beal May 21 '22 at 02:13
  • @EdBeal How do you determine #4 for 50A feeder to a detached building? Wouldn't 250.34(E) apply? – NoSparksPlease May 21 '22 at 02:38
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    An Ufer ground is the best ground rod money can buy. (still not good enough to replace a ground wire.). If you can convince your concrete people to give you an Ufer ground, you don't need ground rods. Ground rods would be stupid. – Harper - Reinstate Monica May 21 '22 at 02:48
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    @nosparksplease ufer grounds require # 4 in my jurisdiction and you could use 8 awg but see comment below. and that is what I was commenting on if smaller than 6 is used it has to be protected in conduit so what ID10t would use smaller for those read the comment both stated the type of that grounding method was used not from the original service as the question asks. – Ed Beal May 21 '22 at 02:53

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Can't say why your inspector would say that unless he understood that it was going to be one 20A circuit, which the Code has an exception which allows a single pole or MWBC (two-pole) 20A without an electrode.

Even if you qualify to not install ground rods you still can.

Where I live concrete encased is required if you are building a new concrete foundation building that requires electrodes. The normal method is to stub a piece of rebar up in a wall and use a J30-db to make the connection in the wall and use an MP2 in the sheetrock and blank cover to make connection accessible.

Edit: Ground rods are one type of electrode that satisfies the grounding electrode requirement. I can only imagine there was a misunderstanding somewhere and that he meant ground rods aren't the only (or preferred) method and I would proceed with providing an electrode for the garage as required by NEC 250.32(A). It would be a whole lot easier to put in an extra exposed piece of rebar than to need it and not have it.

NoSparksPlease
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  • Thanks all for responses. – Brian Kearney May 22 '22 at 12:08
  • So,to be clear- asking concrete contractor to provide a vertical length of rebar securely tied to other sections of rod that extends just above finished elevation and located just below where panel wound be set would be not only preferable but also a better method to protect against lightning strike? Also gather that I would need to use #4 bare copper as electrode conductor size to panel. Does rebar need to be a specific diameter simile to say 5/8 ground rod? – Brian Kearney May 22 '22 at 12:15
  • Sections of bar fastened together by tie wire minimum #4 bar with end of one bar turned up near panel. This page quotes the NEC for all allowed electrode construction. https://www.electricallicenserenewal.com/Electrical-Continuing-Education-Courses/NEC-Content.php?sectionID=991.0 – NoSparksPlease May 22 '22 at 13:59
  • Table 250.66 allows #8 for #2 or smaller copper feeder conductors, but https://up.codes/s/grounding-electrode-conductor-installation (quoted NEC) "smaller than 6 awg" requires specific protection raceways (which could just be 24" of sch80 if directly below panel), #6 or larger that is "exposed to physical damage" also must be protected. "Exposed" can be interpreted broadly by AHJ's, but if in a finished wall no protection may be required. If you are thin skinned be careful not to argue or call your inspector names, interpretations can get very harsh. – NoSparksPlease May 22 '22 at 14:27
  • Also it bears repeating, your State or City may adopt the NEC with modifications, the NEC is owned by the NFPA and has no authority. – NoSparksPlease May 22 '22 at 14:37
  • Thanks for that information. – Brian Kearney May 24 '22 at 11:33
  • One final clarification- Ufer ground are often also call footing ground. My footing has already been poured but the foundation / retaining wall for my garage will have quite a bit of rebar for grounding grid. Can I connect to that as well to satisfy requirement? – Brian Kearney May 24 '22 at 11:34
  • It sounds like you are OK, 250.52(A)(3) says "or within vertical foundations...that are in direct contact with the earth". I think your situation is normal, installing a single piece of bar from footing through foundation to above grade would be difficult. As an addition note I would assume there was some misunderstanding and assume electrodes are still locally required, you should call and verify what portion the inspector want to come out and bless. Sometimes they don't like required but necessary trips, and sometimes photos can satisfy later curiosity. – NoSparksPlease May 24 '22 at 13:21
  • Thx NoSparksPlease. I realized that the footing had rebar protruding that will connect to additional ones for foundation,so that technicality is taken care of. I had read that adding an optional ground rod isn’t advisable as it could provide a second path for potential lightning strike , an not advisable. – Brian Kearney May 25 '22 at 20:17